Fluorine-containing elastomer composition and molded article made of same

ABSTRACT

There is provided a polyol-crosslinkable fluorine-containing elastomer composition which is excellent in chemical resistance, solvent resistance (especially resistance to an acidic solvent) and fuel resistance (especially biofuel resistance) and is crosslinkable at the same crosslinking speed as in the case of using calcium hydroxide in a usual amount even without blending calcium hydroxide (or decreasing a blending amount of calcium hydroxide). The fluorine-containing elastomer composition comprises a polyol-crosslinkable fluorine-containing elastomer, a polyol crosslinking agent and a silicate of an alkali metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 13/054,325filed Jan. 14, 2011, which is a 371 of PCT International Application No.PCT/JP2008/072600 filed on Dec. 5, 2008 and which claims benefit ofJapanese Patent Application No. 2008-186997 filed Jul. 18, 2008. Theabove-noted applications are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a fluorine-containing elastomercomposition and a molded article made of the composition.

BACKGROUND ART

Fluorine-containing elastomers are widely used in the fields ofautomobile industry, semiconductor industry and chemical industrybecause they exhibit excellent chemical resistance, solvent resistanceand heat resistance. For example, in the field of automobile industry,fluorine-containing elastomers are used as a hose, a sealing materialand the like for an engine and peripheral equipment thereof, andautomatic transmission (AT) equipment, fuel system and peripheralequipment thereof.

On the other hand, in compounding of components of fluorine-containingelastomer compositions of a polyol crosslinking system which isgenerally adopted, blending of calcium hydroxide to the compositions hasbeen carried out to accelerate crosslinking (for example, refer toJP52-15543A and Takaomi Satokawa, “Fluorine-containing Resin Handbook”,First Edition, Nikkan Kogyo Shuppan Production, Nov. 30, 1990, p. 567).

However, in a polyol-crosslinkable fluorine-containing elastomercomposition, it is known that when an elastomer molded articlecomprising calcium hydroxide comes into contact with fuels (especiallybiofuels), chemicals and solvents (especially acidic solvents),decomposition and deterioration of such fuels and the like occur. Amongthese fuels and the like, biofuels (for example, biodiesel, etc.)produced from oils derived from living beings is easily oxidized anddeteriorated in the presence of calcium hydroxide, and then apolyol-crosslinkable fluorine-containing elastomer composition aftercoming into contact with the deteriorated biofuel is also greatlysubject to deterioration and swelling. There is no problem when anamount of calcium hydroxide is deceased or it is not blended. However,in the case of using no calcium hydroxide, a crosslinking speed isgreatly decreased, which is not practicable. Therefore, the presentsituation is such that calcium hydroxide is blended.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide apolyol-crosslinkable fluorine-containing elastomer composition which isexcellent in fuel resistance (especially biofuel resistance), chemicalresistance and solvent resistance (especially resistance to an acidicsolvent) and is crosslinkable at the same level of a crosslinking speedas in the case of using a required amount of calcium hydroxide evenwithout blending calcium hydroxide which increases the crosslinkingspeed but accelerates oxidation and deterioration of a fuel.

The present invention relates to a fluorine-containing elastomercomposition comprising a polyol-crosslinkable fluorine-containingelastomer, a polyol crosslinking agent and a silicate of an alkalimetal.

It is preferable that the silicate of an alkali metal is sodium silicateor a salt hydrate thereof.

Further, the present invention relates to a molded article prepared bypolyol-crosslinking the above-mentioned fluorine-containing elastomercomposition.

It is preferable that the molded article is a sealing material,especially a sealing material coming into contact with a biofuel.

It is preferable that the molded article is a fuel hose, especially afuel hose coming into contact with a biofuel.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to the fluorine-containing elastomercomposition comprising a polyol-crosslinkable fluorine-containingelastomer, a polyol crosslinking agent and a silicate of an alkalimetal.

Examples of the polyol-crosslinkable fluorine-containing elastomer whichis used in the present invention are a fluorine-containing vinylidenefluoride (VdF) type elastomer, fluorine-containing tetrafluoroethylene(TFE)/propylene type elastomer, fluorine-containing TFE/propylene/VdFtype elastomer, fluorine-containing ethylene/hexafluoropropylene (HFP)type elastomer, fluorine-containing ethylene/HFP/VdF type elastomer,fluorine-containing ethylene/HFP/TFE type elastomer, fluorine-containingfluorosilicone type elastomer, and fluorine-containing fluorophosphazenetype elastomer. These can be used alone or can be used in an optionalcombination to such an extent not to impair the effects of the presentinvention.

Examples of preferred fluorine-containing VdF type elastomers are thoserepresented by the formula (1).

-(M¹)-(M²)-(N¹)—  (1)

(In the formula, the structural unit M¹ is a structural unit derivedfrom VdF (m¹), the structural unit M² is a structural unit derived froma fluorine-containing ethylenic monomer (m²) other than VdF (m¹ ), andthe structural unit N¹ is a structural unit derived from a monomer (n¹ )being copolymerizable with the monomer (m¹) and the monomer (m²).)

In the fluorine-containing VdF type elastomers represented by theformula (1), assuming that the structural unit M¹+M² is 100% by mole,preferable is one comprising 20 to 85% by mole of the structural unit M¹and 80 to 15% by mole of the structural unit M², and more preferable isone comprising 25 to 80% by mole of the structural unit M¹ and 75 to 20%by mole of the structural unit M². The structural unit N¹ is an optionalstructural unit, and it is preferable that the structural unit N¹ iscontained in an amount of 0 to 10% by mole based on the total amount ofthe structural unit M¹ and the structural unit M².

Examples of the fluorine-containing ethylenic monomer (m²) are one ortwo or more kinds of fluorine-containing monomers such as TFE,chlorotrifluoroethylene (CTFE), trifluoroethylene, HFP,trifluoropropylene, tetrafluoropropylene, pentafluoropropylene,trifluorobutene, tetrafluoroisobutene, fluoro(alkyl vinyl ether),perfluoro(alkyl vinyl ether) (PAVE) and vinyl fluoride. Among these,TFE, HFP, PAVE and a combination thereof are preferred. Examples of PAVEare perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), andthe like.

Any monomer can be used as the monomer (n¹ ) as far as it iscopolymerizable with the monomer (m¹) and the monomer (m²), and, forexample, there are ethylene, propylene, alkyl vinyl ether and the like.

Specific examples of such fluorine-containing VdF type elastomers arepreferably fluorine-containing VdF/HFP type elastomer,fluorine-containing VdF/HFP/TFE type elastomer, fluorine-containingVdF/CTFE type elastomer, fluorine-containing VdF/CTFE/TFE type elastomerand the like.

Examples of preferred fluorine-containing TFE/propylene type elastomersare those represented by the formula (2).

-(M³)-(M⁴)-(N²)—  (2)

(In the formula, the structural unit M³ is a structural unit derivedfrom tetrafluoroethylene (m³), the structural unit M⁴ is a structuralunit derived from propylene (m⁴), and the structural unit N² is astructural unit derived from a monomer (n²) being copolymerizable withthe monomer (m³) and the monomer (m⁴).)

In the fluorine-containing TFE/propylene type elastomers represented bythe formula (2), assuming that the structural unit M³+M⁴ is 100% bymole, preferable is one comprising 40 to 70% by mole of the structuralunit M³ and 60 to 30% by mole of the structural unit M⁴, and morepreferable is one comprising 50 to 60% by mole of the structural unit M³and 50 to 40% by mole of the structural unit M⁴. The structural unit N²is an optional structural unit, and it is preferable that the structuralunit N² is contained in an amount of 0 to 40% by mole based on the totalamount of the structural unit M³ and the structural unit M⁴.

Any monomer other than VdF can be used as the monomer (n²) as far as itis copolymerizable with the monomer (m³) and the monomer (m⁴), andmonomers giving cure site are preferred.

Examples of monomers giving cure site are iodine-containing monomerssuch as perfluoro(6, 6-dihydro-6-iodo-3-oxa-1-hexene) andperfluoro(5-iodo-3-oxa-1-pentene) disclosed in JP5-63482B andJP7-316234A, bromine-containing monomers disclosed in JP4-505341A,cyano-containing monomers, carboxyl-containing monomers andalkoxycarbonyl-containing monomers disclosed in JP4-505345A andJP5-500070A, and the like.

Among the fluorine-containing elastomers, from the viewpoint of heatresistance, compression set, processability and cost,fluorine-containing elastomers comprising VdF unit is more preferable,and a VdF/HFP type elastomer and a VdF/HFP/TFE type elastomer areespecially preferable.

The fluorine-containing elastomer is not limited to one kind, and two ormore kinds may be used.

In addition, the fluorine-containing elastomer which is used in thepresent invention is preferably a fluorine-containing elastomer having afluorine content of not less than 65% by mass, more preferably afluorine-containing elastomer having a fluorine content of not less than66% by mass, from the viewpoint of satisfactory chemical resistance,fuel resistance and fuel impermeability. An upper limit of the fluorinecontent is not limited particularly, and is preferably not more than 74%by mass.

In the present invention, the fluorine-containing elastomer ispolyol-crosslinkable. Processability of the polyol-crosslinkablefluorine-containing elastomer is excellent as compared withprocessability of other crosslinkable fluorine-containing elastomer, andin addition, the molded article obtained by crosslinking in the presenceof a polyol crosslinking agent is low in compression set and isexcellent in heat resistance.

Herein, “crosslinking” means crosslinking of the same or differentpolymer chains of the fluorine-containing elastomer by using acrosslinking agent. By the crosslinking, the fluorine-containingelastomer comes to have improved strength and good elasticity.

In the present invention, compounds known as a crosslinking agent forfluorine-containing elastomers of polyol crosslinking system can be usedas the polyol crosslinking agent to be blended to thefluorine-containing elastomer composition of the present invention, and,for example, polyhydroxy compounds are preferable since moldability isexcellent and the fluorine-containing elastomer molded article obtainedby crosslinking has small compression set, and particularly polyhydroxyaromatic compounds are suitably used from the viewpoint of excellentheat resistance.

The above-mentioned polyhydroxy aromatic compounds are not limitedparticularly, and for example, there are 2,2-bis(4-hydroxyphenyl)propane(hereinafter referred to as bisphenol A),2,2-bis(4-hydroxyphenyl)perfluoropropane (hereinafter referred to asbisphenol AF), resorcin, 1,3-dihydroxybenzene, 1,7-dihydroxynaphthalene, 2, 7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 4, 4′-dihydroxydiphenyl, 4,4′-dihydroxystilbene,2, 6-dihydroxyanthracene, hydroquinone, catechol,2,2-bis(4-hydroxyphenyl)butane (hereinafter referred to as bisphenol B),4, 4-bis(4-hydroxyphenyl)valeric acid, 2, 2-bis(4-hydroxyphenyl)tetrafluorodichloropropane,4,4′-dihydroxydiphenylsulfone, 4,4′-dihydroxydiphenylketone,tri(4-hydroxyphenyl)methane, 3,3′,5,5′-tetrachlorobisphenol A,3,3′,5,5′-tetrabromobisphenol A and the like. Those polyhydroxy aromaticcompounds may be alkali metal salts, alkali earth metal salts and thelike. However in the case where a fluorine-containing elastomer is oneobtained by coagulation using an acid and then separation andcollection, it is preferable not to use the above-mentioned metal saltsin order to prevent a metal from being contained in the composition.

Among these polyhydroxy aromatic compounds, bisphenol AF is especiallypreferable since moldability of the composition is satisfactory and thefluorine-containing elastomer molded article obtained by crosslinking issmall in compression set and is excellent in heat resistance.

The amount of polyol crosslinking agent is preferably 0.2 to 10 parts bymass, more preferably 0.5 to 6 parts by mass, further preferably 1 to 3parts by mass based on 100 parts by mass of the fluorine-containingelastomer. When the amount of crosslinking agent is less than 0.2 partby mass, there is a tendency that crosslinking density of the obtainedmolded article is low, and its compression set is increased. When theamount of crosslinking agent exceeds 10 parts by mass, there is atendency that since crosslinking density of the obtained molded articlebecomes too high, it is easily broken at compression.

The fluorine-containing elastomer composition of the present inventioncomprises a silicate of an alkali metal. By blending the silicate of analkali metal to the composition, polyol-crosslinking can be carried outin the same period of time as in the case of blending conventionalcalcium hydroxide even without blending calcium hydroxide. In addition,by blending the silicate of an alkali metal to the composition, since itis not necessary to blend calcium hydroxide for accelerating acrosslinking speed, deterioration and swelling of the obtained moldedarticle which occur due to contact with a chemical, a solvent(especially an acidic solvent) or a fuel (especially a biofuel) can bedecreased and in addition, improvement in compression set can beexpected.

Examples of a silicate of an alkali metal are sodium silicate, potassiumsilicate, lithium silicate, and salt hydrates thereof.

In the case where the silicate of an alkali metal is sodium silicate orits salt hydrate, the composition of sodium silicate or its salt hydrateis represented by a mass ratio (%) of Na2O, SiO2 and H2O, and ispreferably 0.5 to 95% by mass of Na2O, 5 to 99% by mass of SiO2 and 0 to94.5% by mass of H2O. In addition, from the viewpoint of an excellenteffect of increasing a crosslinking speed, 1 to 85% by mass of Na2O, 2.0to 95% by mass of SiO2 and 0 to 85% by mass of H₂O is more preferable.Further, from the viewpoint of excellent processability, 2 to 70% bymass of Na2O, 7.0 to 70% by mass of SiO2 and 0 to 75% by mass of H₂O isfurther preferable.

Examples of commercially available sodium silicate or its salt hydrateare, for instance, Sodium Silicate No. 1 to No. 5 (available from FujiKagaku Corp.), sodium metasilicate, 5hydrate and sodium metasilicate,9hydrate (available from Fuji Kagaku Corp.), sodium orthosilicate (65%,80%) (available from Osaka Keisou Co., Ltd.), Sodium Silicate Powder No.1 to No. 3 (available from Nippon Chemical Industrial Co., Ltd.) andanhydrous sodium silicate (available from Osaka Keisou Co., Ltd.).

In the case where the silicate of an alkali metal is a salt hydrate ofpotassium silicate, the composition of a salt hydrate of potassiumsilicate is represented by a mass ratio (%) of K2O, SiO2 and H2O, and ispreferably 5 to 30% by mass of K2O, 15 to 35% by mass of SiO2 and 35 to80% by mass of H2O.

Examples of commercially available salt hydrate of potassium silicateare, for instance, potassium silicate No. 1 and potassium silicate No. 2(available from Fuji Kagaku Corp.).

In the case where the silicate of an alkali metal is a salt hydrate oflithium silicate, the composition of a salt hydrate of lithium silicateis represented by a mass ratio (%) of Li2O, SiO2 and H2O, and ispreferably 0.5 to 10% by mass of Li2O, 15 to 25% by mass of SiO2 and 65to 84.5% by mass of H2O.

Examples of commercially available salt hydrate of lithium silicate are,for instance, Lithium silicate 45 (available from Nippon ChemicalIndustrial Co., Ltd.).

Among these silicates of an alkali metal, sodium silicate or its salthydrate is preferable since stable crosslinking speed can be obtainedand fuel resistance is satisfactory.

The amount of silicate of an alkali metal is preferably 0.1 to 10 partsby mass, more preferably 0.2 to 7 parts by mass based on 100 parts bymass of the fluorine-containing elastomer.

In the present invention, the use of calcium hydroxide is notnecessarily excluded, but the use of calcium hydroxide should beinhibited to an extent not to affect the advantages and effectsexhibited by the use of the silicate of an alkali metal. The amount ofcalcium hydroxide should be less than the amount of silicate of analkali metal contained in the fluorine-containing elastomer composition,and concretely should be not more than 3 parts by mass, further not morethan 1 part by mass based on 100 parts by mass of thefluorine-containing elastomer. It is especially preferable that calciumhydroxide is not blended substantially.

A crosslinking accelerator, an acid acceptor, a crosslinking aid and aco-crosslinking agent may be blended to the composition as additivesrelating to the crosslinking other than the above-mentioned polyolcrosslinking agent and silicate of an alkali metal.

When a crosslinking accelerator is used, formation of intermoleculardouble bond by dehydrofluorination reaction of a trunk chain of thefluorine-containing elastomer is accelerated, thereby enablingcrosslinking reaction to be accelerated.

The crosslinking accelerator is not limited particularly, and oniumsalts can be used.

Onium salts are not limited particularly, and preferred examples thereofare, for instance, quaternary ammonium salts, quaternary phosphoniumsalts, oxonium salts, sulfonium salts, cyclic amines, mono-functionalamine compounds and the like. Among these, quaternary ammonium salts andquaternary phosphonium salts are preferable.

The quaternary ammonium salt is not limited particularly, and examplesthereof are, for instance, salts of 1,8-diazabicyclo[5,4,0]-7-undeceniumderivative such as8-methyl-1,8-diazabicyclo[5,4,01]-7-undeceniumchloride,8-methyl-1,8-diazabicyclo[5,4,01]-7-undeceniumiodide,8-methyl-1,8-diazabicyclo[5,4,0]-7-undeceniumhydroxide,8-methyl-1,8-diazabicyclo[5,4, 0]-7-undeceniummethylsulfate,8-ethyl-1,8-diazabicyclo[5,4,0]-7-undeceniumbromide,8-propyl-1,8-diazabicyclo[5,4,0]-7-undeceniumbromide, 8-dodecyl-1,8-diazabicyclo[5,4,0]-7-undeceniumchloride, 8-dodecyl-1,8-diazabicyclo[5,4,0]-7-undeceniumhydroxide, 8-eicosyl-1,8-diazabicyclo[5,4,0]-7-undeceniumchloride, 8-tetracosyl-1,8-diazabicyclo[5,4,0]-7-undeceniumchloride,8-benzyl-1,8-diazabicyclo[5,4,0]-7-undeceniumchloride (hereinafterreferred to as DBU-B), 8-benzyl-1, 8-diazabicyclo[5 ,4, 0]-7-undeceniumhydroxide, 8-phenetyl-1, 8-diazabicyclo[5 ,4, 0]-7-undeceniumchloride,8-(3-phenylpropyl)-1,8-diazabicyclo[5,4,0]-7-undeceniumchloride and thelike. Among these, 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium saltand DBU-B are preferable from the viewpoint of satisfactorycrosslinkability and physical properties of a crosslinked product.

The quaternary phosphonium salt is not limited particularly, andexamples thereof are, for instance, tetrabutylphosphonium chloride,benzyltriphenylphosphonium chloride (hereinafter referred to as BTPPC),benzyltrimethylphosphonium chloride, benzyltributylphosphonium chloride,tributylallylphosphonium chloride, tributyl-2-methoxypropylphosphoniumchloride, benzylphenyl(dimethylamino)phosphonium chloride and the like.Among these, BTPPC is preferable from the viewpoint of satisfactorycrosslinkability and physical properties of a crosslinked product.

In addition, solid solutions of quaternary phosphonium salts andbisphenol AF, and compounds disclosed in JP11-147891A can be used.

Also, two or more kinds of onium salts may be used.

The amount of crosslinking accelerator is preferably 0.1 to 5.0 parts bymass, more preferably 0.2 to 2 parts by mass, further preferably 0.3 to1.5 parts by mass based on 100 parts by mass of the fluorine-containingelastomer since a crosslinking speed, physical properties in normalstate of a molded article and compression set are easily adjusted.

An acid acceptor is one used for removing an acidic substance to begenerated at the polyol crosslinking, and examples thereof are magnesiumoxide, calcium oxide, litharge (lead oxide), zinc oxide, dibasicphosphite, hydrotalcite and the like.

When magnesium oxide is used as an acid acceptor, its amount ispreferably not less than 0.1 part by mass, more preferably not less than0.5 part by mass, further preferably not less than 1 part by mass basedon 100 parts by mass of the fluorine-containing elastomer since there isan excellent effect of accepting hydrogen fluoride to be generated inthe crosslinking reaction. In addition, from the viewpoint ofsatisfactory chemical resistance, the amount is preferably not more than10 parts by mass, more preferably not more than 5 parts by mass based on100 parts by mass of the fluorine-containing elastomer.

In addition, it is possible to blend, to the fluorine-containingelastomer composition of the present invention, usual additives to beblended to fluorine-containing elastomer compositions as case demands,for example, a filler, a processing aid, a plasticizer, a colorant, astabilizer, an adhesion aid, a mold releasing agent, an electricconductivity imparting agent, a thermal conductivity imparting agent, anagent for imparting surface non-adhesiveness, a flexibility impartingagent, a heat resistance improver, a flame retardant and the like.

The fluorine-containing elastomer composition of the present inventioncan be obtained by kneading the polyol-crosslinkable fluorine-containingelastomer, polyol crosslinking agent, silicate of an alkali metal, andother compounding agents to be blended as case demands such as acrosslinking accelerator and an acid acceptor by using a rubber kneadingequipment generally used. A roll, kneader, Banbury mixer, internalmixer, twin screw extruder or the like can be used as the rubberkneading equipment.

Many of polyol crosslinking agents and crosslinking accelerators haverelatively high melting point. Therefore, when using a crosslinkingagent together with a crosslinking accelerator, in order to uniformlydisperse them in the fluorine-containing elastomer, there is preferablyused a method of kneading a crosslinking agent and a crosslinkingaccelerator while melting them at high temperature of 100° to 150° C. byusing a closed kneading equipment such as a kneader and then kneadingtogether with the fluorine-containing elastomer and if necessary, othercompounding agents such as a filler at a temperature lower than thetemperature mentioned above. In addition, there is a method of, aftermixing a polyol crosslinking agent and a crosslinking accelerator,melting them and forming the mixture into a solid solution having alowered melting point and then uniformly dispersing by using theobtained solid solution.

Dispersibility can be further increased by kneading thefluorine-containing elastomer composition, allowing to stand at roomtemperature for 12 hours or more and then carrying out kneading again.

The present invention also relates to the molded article obtained bypolyol-crosslinking the above-mentioned fluorine-containing elastomercomposition.

The molded article of the present invention is prepared by molding andpolyol-crosslinking the above-mentioned fluorine-containing elastomercomposition. The polyol-crosslinking can be carried out under anyconditions such as under normal pressure, under pressure, under reducedpressure or in the air.

For crosslinking, usual methods such as press crosslinking and steamcrosslinking can be employed. Crosslinking conditions may be optionallydetermined depending on kind and amount of fluorine-containing polymer,polyol crosslinking agent, and silicate of an alkali metal, and usuallycrosslinking is carried out at 100° to 200° C. for 5 to 60 minutes.Further, when the crosslinking needs be completed, secondarycrosslinking may be conducted.

In the present invention, by blending the silicate of an alkali metal,polyol-crosslinking can be carried out in the same period of time as inthe case of using calcium hydroxide even without blending calciumhydroxide.

Since the molded article of the present invention comprises the silicateof an alkali metal, it is not necessary to blend calcium hydroxide foraccelerating a crosslinking speed. Therefore, deterioration and swellingof the obtained molded article which occur due to contact with achemical, a solvent (especially an acidic solvent) or a fuel (especiallya biofuel) can be decreased, and in addition, improvement in compressionset can be expected. In addition, since the molded article has heatresistance, it is useful as a sealing material and a fuel hose,especially as a sealing material and a fuel hose for an engine andperipheral equipment thereof, AT equipment, a fuel system and peripheralequipment thereof of automobiles.

Application of the molded article of the present invention as thesealing material is not limited particularly, and examples are, forinstance, sealing materials such as gaskets and non-contact type andcontact type packings (self-seal packing, piston ring, split ringpacking, mechanical seal, oil seal, etc.) which are required to haveheat resistance, oil resistance, fuel oil resistance, resistance to ananti-freezing fluid for cooling an engine and steam resistance and areused for automobile engine such as engine body, main engine-drivingsystem, engine-driving valve system, lubricating and cooling system,fuel system, and suction/exhaust system; transmission of drive system;steering system of chassis; brake system; standard electrical parts forinstrumentation, electrical parts for control and equipped electricalparts.

Sealing materials used on an engine body of automobiles are not limitedparticularly, and examples thereof are, for instance, gaskets such as acylinder head gasket, cylinder head cover gasket, oil pan packing andgeneral gaskets, and sealing materials such as an O-ring, packing andtiming belt cover gasket.

Sealing materials used on a main drive system of an automobile engineare not limited particularly, and examples thereof are, for instance,shaft seals such as crank shaft seal and cam shaft seal.

Sealing materials used on valves of an automobile engine are not limitedparticularly, and examples thereof are, for instance, a valve stem oilseal of an engine valve.

Sealing materials used on a lubricating and cooling system of anautomobile engine are not limited particularly, and examples thereofare, for instance, a seal gasket for an engine oil cooler and the like.

Sealing materials used on a fuel system of an automobile engine are notlimited particularly, and examples thereof are, for instance, an oilseal of a fuel pump, a filler seal and tank packing of a fuel tank, aconnector O-ring of a fuel tube, an injector cushion ring, an injectorseal ring and an injector O-ring of a fuel injector, a flange gasket ofa carburetor and the like.

Sealing materials used on a suction/exhaust system of an automobileengine are not limited particularly, and examples thereof are, forinstance, a suction manifold packing and exhaust manifold packing of amanifold, a throttle body packing, a turbine shaft seal of a turbocharger and the like.

Sealing materials used on a transmission system of an automobile engineare not limited particularly, and examples thereof are, for instance, abearing seal, oil seal, O-ring and packing for transmission and anO-ring and packing for automatic transmission (AT).

Sealing materials used on a brake system of an automobile engine are notlimited particularly, and examples thereof are, for instance, an oilseal, O-ring, packing, piston cup (rubber cup) of a master cylinder,caliper seal, boots and the like.

Sealing materials used on electrical parts of an automobile engine arenot limited particularly, and examples thereof are, for instance, anO-ring and packing of an air conditioner.

Applications of the sealing material other than automobile applicationare not limited particularly, and examples thereof are, for instance,packing, O-ring and other sealing materials requiring oil resistance,chemical resistance, heat resistance, steam resistance and weatherresistance for transport means such as ships and air planes; similarpacking, O-ring and other sealing materials for chemical plants; similarpacking, O-ring and other sealing materials for food plant equipment andfood processing equipment (including those for domestic use); similarpacking, O-ring and other sealing materials for equipment of atomicpower plant; and similar packing, O-ring and other sealing materials forgeneral industrial parts.

The molded article of the present invention is suitably used as hoses(including tubes) for the above-mentioned various applications of thesealing material, equipment and parts, and is suitable especially ashoses for industrial use and fuel hoses.

The molded article of the present invention is also useful for moldedarticles such as sealing materials and hoses coming into contact withfuels derived from plants such as maize and soy bean, i.e., so-calledbiofuels. Among biofuels, especially in the case of a biodiesel fuel,when it is used under harsh conditions where fossil fuels are used,there is a case where various components and impurities derived fromliving beings are subject to decomposition and chemical change such asoxidation and deterioration, resulting in deterioration and swelling ofvarious metal, resin and rubber members coming into contact with suchfuels. The molded article of the present invention is hardly subject todeterioration and swelling even if it contacts a biofuel in whichvarious components and impurities derived from living beings havesuffered from decomposition and chemical change such as oxidation anddeterioration, and therefore, can be used as various members such assealing materials and fuel hoses for biofuels.

“Biofuel” means fuels prepared from living beings, and example thereofare liquid fuels, for instance, bio-alcohols such as biomethanol andbioethanol; biogasoline prepared by mixing bioalcohol and gasoline;ETBE-mixed gasoline comprising gasoline and ethyl tertiary butyl ether(ETBE) which is a reaction product of bioethanol and isobutene; andbiodiesel fuel. Also, biofuels include not only these fuels used forpower source but also fuels for heating. In addition, the use of fossilfuel together is not excluded.

EXAMPLE

The present invention is then explained by means of Examples andComparative Examples, but is not limited to those Examples.

Each chemical used in Examples and Comparative Examples is as follows.

-   Fluorine-containing elastomer A: Polyol-crosslinkable    fluorine-containing elastomer comprising two monomers (VdF/HFP=78/22    (mole %), fluorine content: 66% by mass, Mooney viscosity    ML1+10(100° C.): 45)-   Fluorine-containing elastomer B: Polyol-crosslinkable    fluorine-containing elastomer comprising three monomers    (VdF/TFE/HFP=58/22/20 (mole %), fluorine content: 69% by mass,    Mooney viscosity ML1+10(100° C.): 42)-   Polyol crosslinking agent: 2,2-bis(4-hydroxyphenyl)perfluoropropane    (Bisphenol AF)    Crosslinking accelerator:-   8-benzyl-1 ,8-diazabicyclo[5 ,4, 0]-7-undeceniumchloride (DBU-B)-   Crosslinking accelerator: Crosslinking accelerator (VC50) available    from Du Pont Performance Elastomers, a blend of bisphenol AF and    benzyltriphenylphosphonium salt of bisphenol AF-   Carbon black 1: Carbon black (MT-C) available from Cancarb Co., Ltd.-   Carbon black 2: Carbon black (SEAST S) available from Tokai Carbon    Co., Ltd.-   Magnesium oxide: Magnesium oxide (MA150) available from Kyowa-   Chemical Industries, Co., Ltd.-   Calcium hydroxide: Calcium hydroxide (CALDIC #2000) available from    Ohmi Chemical Industry Co., Ltd.-   Salt hydrate of sodium silicate No. 1: Sodium silicate No. 1    available from Fuji Kagaku Corp., Na2O=15% by mass, SiO2=32% by    mass, H₂O=53% by mass-   Salt hydrate of sodium silicate No. 2: Sodium silicate No. 2    available from Fuji Kagaku Corp., Na2O=12% by mass, SiO2=28% by    mass, H₂O=60% by mass-   Salt hydrate of sodium silicate No. 3: Sodium silicate No. 3    available from AGC Si-Tech. Co., Ltd., Na2O=10% by mass, SiO2=29% by    mass, H₂O=61% by mass-   Salt hydrate of sodium silicate No. 5: Sodium silicate No. 5    available from Fuji Kagaku Corp., Na2O=7% by mass, SiO2=26% by mass,    H₂O=67% by mass-   Sodium metasilicate, 5hydrate: Sodium metasilicate, 5hydrate    available from Fuji Kagaku Corp., Na2O=30% by mass, SiO2=29% by    mass, H₂O=41% by mass-   Salt hydrate of 65% sodium orthosilicate: 65% sodium orthosilicate    available from Osaka Keisou Co., Ltd., Na2O=43% by mass, SiO2=22% by    mass, H₂O=35% by mass-   Salt hydrate of potassium silicate No. 1: Potassium silicate No. 1    available from Fuji Kagaku Corp., K2O=22% by mass, SiO2=28% by mass,    H₂O=50% by mass-   Salt hydrate of potassium silicate No. 2: Potassium silicate No. 2    available from Fuji Kagaku Corp., K2O=9% by mass, SiO2=20.5% by    mass, H₂O=70.5% by mass-   Salt hydrate of lithium silicate: Lithium silicate 45 available from    Nippon Chemical Industrial Co., Ltd., Li2O=2.5% by mass, SiO2=21% by    mass, H₂O=76.5% by mass-   Magnesium silicate: AD600 available from Tomita Pharmaceutical Co.,    Ltd.-   Calcium silicate: AD850H200M available from Tomita Pharmaceutical    Co., Ltd.-   Aluminum silicate: AD700 available from Tomita Pharmaceutical Co.,    Ltd.

Example 1

To 100 parts by mass of fluorine-containing elastomer A were mixed 1.5parts by mass of bisphenol AF as a crosslinking agent and 0.3 part bymass of DBU-B as a crosslinking accelerator, and the mixture was kneadedwith an open roll. Thereto were added Carbon black 1, magnesium oxideand salt hydrate of sodium silicate No. 1 in the proportions shown inTable 1, followed by kneading with an open roll to prepare acrosslinkable fluorine-containing elastomer composition. Then, thecomposition was formed into an about 2 mm thick sheet to prepare anun-crosslinked rubber sheet. Crosslinking characteristics of theobtained un-crosslinked rubber sheet were measured by the followingmethods. Proportions (parts by mass) of the components of thefluorine-containing elastomer composition are shown in Table 1, and theresults of evaluation of the crosslinking characteristics are shown inTable 2.

<Crosslinking Characteristics>

A crosslinking curve of an un-crosslinked rubber sheet is examined at acrosslinking temperature shown in Table 2 according to JIS K6300-2 byusing a rubber processability analyzer RPA2000 (available from AlphaTechnologies, Japan LLC) to determine induction time (T10), 90%crosslinking time (T90), maximum torque (ML) and minimum torque (MH).

Then, the obtained un-crosslinked rubber sheet is subjected to presscrosslinking at a temperature and time shown in Table 2 and furtherheating in an oven at a temperature and time shown in Table 2 (secondarycrosslinking) to obtain a 2 mm thick crosslinked rubber sheet as acrosslinked molded article.

Heating characteristics and resistance to biodiesel fuel of thiscrosslinked rubber sheet are measured by the following methods. Theresults of evaluation are shown in Table 2.

<Heating Characteristics >

Compression set (CS) is measured at 200° C. for 72 hours by 25%compression according to JIS B2401.

<Resistance to Biodiesel Fuel>

A volume of a crosslinked rubber sheet before dipping is measured. Then,the crosslinked rubber sheet is dipped in a deteriorated biodiesel fuel(SME (soybean methyl ester) fuel (NEXSOL BD-0100 BIODIESEL availablefrom PETER CREMER): 2% by volume of water is contained) at 125° C. for504 hours. A volume of the crosslinked rubber sheet after the dipping ismeasured, and a rate of change in volume (%) is determined.

Examples 2 to 9

Un-crosslinked rubber sheets were prepared in the same manner as inExample 1 except that salt hydrate of sodium silicate No. 2 (Example 2),salt hydrate of sodium silicate No. 3 (Example 3), salt hydrate ofsodium silicate No. 5 (Example 4), sodium metasilicate, 5hydrate(Example 5), salt hydrate of 65% sodium orthosilicate (Example 6), salthydrate of potassium silicate No. 1 (Example 7), salt hydrate ofpotassium silicate No. 2 (Example 8) and salt hydrate of lithiumsilicate (Example 9) were used respectively in amounts shown in Table 1instead of salt hydrate of sodium silicate No. 1, and crosslinkingcharacteristics of the obtained un-crosslinked rubber sheets weremeasured. The results of evaluation are shown in Table 2.

Then, crosslinked rubber sheets were prepared by crosslinking theun-crosslinked rubber sheets under the same crosslinking conditions asin Example 1, and physical properties were measured. Proportions (partsby mass) of the components of the fluorine-containing elastomercompositions are shown in Table 1, and the results of evaluation areshown in Table 2.

Example 10

To 100 parts by mass of fluorine-containing elastomer B were mixed 2parts by mass of a crosslinking agent (bisphenol AF) and 0.6 part bymass of a crosslinking accelerator (DBU-B), and the mixture was kneadedwith an open roll. Thereto were added Carbon black 2, salt hydrate ofsodium silicate No. 1 and magnesium oxide in amounts shown in Table 1,followed by kneading. An un-crosslinked rubber sheet was prepared in thesame manner as in Example 1, and crosslinking characteristics of theobtained un-crosslinked rubber sheet were examined. The results ofevaluation are shown in Table 2.

Then, the un-crosslinked rubber sheet was subjected to crosslinkingunder the crosslinking conditions shown in Table 2 (no secondarycrosslinking was carried out) to prepare a crosslinked molded article(crosslinked rubber sheet), and physical properties were measured. Withrespect to heating characteristics, compression set (CS) was measured at100° C. for 72 hours by 25% compression according to JIS B2401.Proportions (parts by mass) of the components of the fluorine-containingelastomer composition are shown in Table 1, and the results ofevaluation are shown in Table 2.

Example 11

To 100 parts by mass of fluorine-containing elastomer B were mixed 2parts by mass of a crosslinking agent (bisphenol AF) and 0.6 part bymass of a crosslinking accelerator (DBU-B), and the mixture was kneadedwith an open roll. Thereto were added Carbon black 2, salt hydrate ofpotassium silicate No. 1 and magnesium oxide in amounts shown in Table1, followed by kneading. An un-crosslinked rubber sheet was prepared inthe same manner as in Example 1, and crosslinking characteristics of theobtained un-crosslinked rubber sheet were examined. The results ofevaluation are shown in Table 2.

Then, the un-crosslinked rubber sheet was subjected to crosslinkingunder the crosslinking conditions shown in Table 2 (no secondarycrosslinking was carried out) to prepare a crosslinked molded article(crosslinked rubber sheet), and physical properties were measured. Withrespect to heating characteristics, compression set (CS) was measured at100° C. for 72 hours by 25% compression according to JIS B2401.Proportions (parts by mass) of the components of the fluorine-containingelastomer composition are shown in Table 1, and the results ofevaluation are shown in Table 2.

Example 12

To 100 parts by mass of fluorine-containing elastomer A were mixed 1part by mass of a crosslinking agent (bisphenol AF) and 1.5 parts bymass of a crosslinking accelerator (VC50), and the mixture was kneadedwith an open roll. Thereto were added Carbon black 1, sodiummetasilicate, 5hydrate and magnesium oxide in amounts shown in Table 1,followed by kneading. An un-crosslinked rubber sheet was prepared in thesame manner as in Example 1, and crosslinking characteristics of theobtained un-crosslinked rubber sheet were measured. The results ofevaluation are shown in Table 2.

Then, the un-crosslinked rubber sheet was subjected to crosslinkingunder the same crosslinking conditions as in Example 1 to prepare acrosslinked molded article (crosslinked rubber sheet), and physicalproperties were measured. Proportions (parts by mass) of the componentsof the fluorine-containing elastomer composition are shown in Table 1,and the results of evaluation are shown in Table 2.

Examples 13 and 14

Un-crosslinked rubber sheets were prepared in the same manner as inExample 12 except that salt hydrate of 65% sodium orthosilicate (Example13) and salt hydrate of lithium silicate (Example 14) were used insteadof sodium metasilicate, 5hydrate, and crosslinking characteristics ofthe obtained un-crosslinked rubber sheets were examined. The results ofevaluation are shown in Table 2.

Then, the un-crosslinked rubber sheets were subjected to crosslinkingunder the same crosslinking conditions as in Example 1 to preparecrosslinked molded articles (crosslinked rubber sheets), and physicalproperties were measured. Proportions (parts by mass) of the componentsof the fluorine-containing elastomer composition are shown in Table 1,and the results of evaluation are shown in Table 2.

TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Fluorine- containingelastomer A 100 100 100 100 100 100 100 100 100 — — 100 100 100 B — — —— — — — — — 100 100 — — — Crosslinking agent Bisphenol AF 1.5 1.5 1.51.5 1.5 1.5 1.5 1.5 1.5 2 2 1 1 1 Crosslinking accelerator DBU-B 0.3 0.30.3 0.3 0.3 0.3 0.3 0.3 0.3 0.6 0.6 — — — VC50 — — — — — — — — — — — 1.51.5 1.5 Acid acceptor Magnesium oxide 3 3 3 3 3 3 3 3 3 3 3 3 3 3 FillerCarbon black 1 20 20 20 20 20 20 20 20 20 — — 20 20 20 Carbon black 2 —— — — — — — — — 13 13 — — — Silicate of alkali metal Salt hydrate 3 — —— — — — — — 3 — — — — of sodium silicate No. 1 Salt hydrate — 3 — — — —— — — — — — — — of sodium silicate No. 2 Salt hydrate — — 3 — — — — — —— — — — — of sodium silicate No. 3 Salt hydrate — — — 3 — — — — — — — —— — of sodium silicate No. 5 Sodium — — — — 0.5 — — — — — — 0.5 — —metasilicate, 5hydrate Salt hydrate — — — — — 0.5 — — — — — — 0.5 — of65% sodium orthosilicate Salt hydrate — — — — — — 3 — — — 2 — — — ofpotassium silicate No. 1 Salt hydrate — — — — — — — 3 — — — — — — ofpotassium silicate No. 2 Salt hydrate — — — — — — — — 3 — — — — 3 oflithium silicate

TABLE 2 Example 1 2 3 4 5 6 7 Crosslinking characteristics Temperature(° C.) 170 170 170 170 170 170 170 ML (kgf) 0.1 0.1 0.1 0.1 0.2 0.2 0.3MH (kgf) 2.9 2.6 2 2.2 3 2.8 3.3 T10 (min) 1.6 1.7 2.8 2.4 2.5 2.1 0.8T90 (min) 2.3 2.5 4.4 3.9 4.9 3.1 1.7 Crosslinking conditions PressCrosslinking 170° C. × 170° C. × 170° C. × 170° C. × 170° C. × 170° C. ×170° C. × 10 min 10 min 10 min 10 min 10 min 10 min 10 min Secondary230° C. × 230° C. × 230° C. × 230° C. × 230° C. × 230° C. × 230° C. ×Crosslinking 24 hr 24 hr 24 hr 24 hr 24 hr 24 hr 24 hr Heatingcharacteristics CS (200° C. × 72 hr) 19 18 20 19 18 17 20 CS (100° C. ×72 hr) — — — — — — — Resistance to 7 6 5 6 7 8 6 biodiesel fuel Example8 9 10 11 12 13 14 Crosslinking characteristics Temperature (° C.) 170170 160 160 170 170 170 ML (kgf) 0.2 0.1 0.3 0.3 0.2 0.2 0.1 MH (kgf)2.9 1.8 1.9 2 3.3 3.3 2.7 T10 (min) 1.9 2.2 4.9 4.2 1.4 1.3 1.2 T90(min) 3.2 4.5 12.5 13.5 2.5 2.4 1.4 Crosslinking conditions PressCrosslinking 170° C. × 170° C. × 160° C. × 160° C. × 170° C. × 170° C. ×170° C. × 10 min 10 min 45 min 45 min 10 min 10 min 10 min Secondary230° C. × 230° C. × — — 230° C. × 230° C. × 230° C. × Crosslinking 24 hr24 hr 24 hr 24 hr 24 hr Heating characteristics CS (200° C. × 72 hr) 2019 — — 13 12 16 CS (100° C. × 72 hr) — — 20 16 — — — Resistance to 10 84 7 5 5 5 biodiesel fuel

Comparative Examples 1 and 2

Un-crosslinked rubber sheets were prepared in the same manner as inExample 1 except that calcium hydroxide was used in an amount shown inTable 3 instead of salt hydrate of sodium silicate No. 1, andcrosslinking characteristics of the obtained un-crosslinked rubbersheets were examined. The results of evaluation are shown in Table 4.

Then, the un-crosslinked rubber sheets were subjected to crosslinkingunder the same crosslinking conditions as in Example 1 to preparecrosslinked molded articles (crosslinked rubber sheets), and physicalproperties were measured. Proportions (parts by mass) of the componentsof the fluorine-containing elastomer compositions are shown in Table 3,and the results of evaluation are shown in Table 4.

Comparative Example 3

An un-crosslinked rubber sheet was prepared in the same manner as inExample 1 except that magnesium silicate was used instead of salthydrate of sodium silicate No. 1. The obtained un-crosslinked rubbersheet was subjected to press crosslinking, but was not crosslinked andremained un-crosslinked.

Comparative Example 4

An un-crosslinked rubber sheet was prepared in the same manner as inExample 1 except that calcium silicate was used in an amount shown inTable 3 instead of salt hydrate of sodium silicate No. 1, andcrosslinking characteristics of the obtained un-crosslinked rubber sheetwere examined. The results of evaluation are shown in Table 4.

Then, the un-crosslinked rubber sheet was subjected to crosslinkingunder the same crosslinking conditions as in Example 1 to preparecrosslinked molded article (crosslinked rubber sheet), and physicalproperties were measured. Proportions (parts by mass) of the componentsof the fluorine-containing elastomer composition are shown in Table 3,and the results of evaluation are shown in Table 4.

Comparative Examples 5 to 7

Un-crosslinked rubber sheets were prepared in the same manner as inExample 1 except that aluminum silicate (Comparative Example 5),magnesium silicate and pure water (Comparative Example 6) and calciumsilicate and pure water (Comparative Example 7) were used instead ofsalt hydrate of sodium silicate No. 1. The obtained un-crosslinkedrubber sheets were subjected to press crosslinking, but were notcrosslinked and remained un-crosslinked.

Comparative Examples 8 and 9

To 100 parts by mass of fluorine-containing elastomer B were mixed 2parts by mass of a crosslinking agent (bisphenol AF) and 0.6 part bymass of a crosslinking accelerator (DBU-B), and the mixture was kneadedwith an open roll. Thereto were added Carbon black 2, calcium hydroxideand magnesium oxide in amounts shown in Table 3, followed by kneading.Un-crosslinked rubber sheets were prepared in the same manner as inComparative Example 1, and crosslinking characteristics of the obtainedun-crosslinked rubber sheets were examined. The results of evaluationare shown in Table 4.

Then, the un-crosslinked rubber sheets were subjected to crosslinkingunder the crosslinking conditions shown in Table 4 (no secondarycrosslinking was carried out) to prepare crosslinked molded articles(crosslinked rubber sheets), and physical properties were measured. Withrespect to heating characteristics, compression set (CS) was measured at100° C. for 72 hours by 25% compression according to JIS B2401.Proportions (parts by mass) of the components of the fluorine-containingelastomer compositions are shown in Table 3, and the results ofevaluation are shown in Table 4.

Comparative Examples 10 and 11

To 100 parts by mass of fluorine-containing elastomer A were mixed 1part by mass of a crosslinking agent (bisphenol AF) and 1.5 parts bymass of a crosslinking accelerator (VC50), and the mixture was kneadedwith an open roll. Thereto were added Carbon black 1, calcium hydroxideand magnesium oxide in amounts shown in Table 3, followed by kneading.Un-crosslinked rubber sheets were prepared in the same manner as inComparative Example 1, and crosslinking characteristics of the obtainedun-crosslinked rubber sheets were examined. The results of evaluationare shown in Table 4.

Then, the un-crosslinked rubber sheets were subjected to crosslinkingunder the same crosslinking conditions as in Example 1 to preparecrosslinked molded articles (crosslinked rubber sheets), and physicalproperties were measured. Proportions (parts by mass) of the componentsof the fluorine-containing elastomer compositions are shown in Table 3,and the results of evaluation are shown in Table 4.

TABLE 3 Comparative Example 1 2 3 4 5 6 7 8 9 10 11 Fluorine-containingelastomer A 100 100 100 100 100 100 100 — — 100 100 B — — — — — — — 100100 — — Crosslinking agent Bisphenol AF 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2 21 1 Crosslinking accelerator DBU-B 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.6 0.6 —— VC50 — — — — — — — — — 1.5 1.5 Acid acceptor Magnesium oxide 3 3 3 3 33 3 3 3 3 3 Filler Carbon black 1 20 20 20 20 20 20 20 — — 20 20 Carbonblack 2 — — — — — — — 13 13 — — Metal compound Calcium hydroxide 6 3 — —— — — 6 3 6 3 Magnesium silicate — — 3 — — 1.5 — — — — — Calciumsilicate — — — 3 — — 1.5 — — — — Aluminum silicate — — — — 3 — — — — — —Pure water — — — — — 1.5 1.5 — — — —

TABLE 4 Comparative Example 1 2 3 4 5 6 7 8 9 10 11 Crosslinkingcharacteristics Temperature (° C.) 170 170 170 170 170 170 170 160 160170 170 ML (kgf) 0.2 0.1 not 0.2 not not not 0.3 0.3 0.2 0.2 MH (kgf)2.7 2.3 cross- 1.9 cross- cross- cross- 1.8 1.8 3.2 2.8 T10 (min) 2.94.6 linked 6.7 linked linked linked 5.0 10.7 1.8 2.3 T90 (min) 4.3 7.115.8 10.0 18.7 2.7 3.5 Crosslinking conditions Press Crosslinking 170°C. × 170° C.× — 170° C. × — — — 160° C.× 160° C. × 170° C. × 170° C. ×10 min 10 min 10 min 45 min 45 min 10 min 10 min Secondary 230° C. ×230° C. × — 230° C. × — — — — — 230° C. × 230° C. × Crosslinking 24 hr24 hr 24 hr 24 hr 24 hr Heating characteristics CS (200° C. × 72 hr) 2222 — 25 — — — — — 17 16 CS (100° C. × 72 hr) — — — — — — — 24 22 — —Resistance to 93 55 — 27 — — — 110 55 78 45 biodiesel fuel

INDUSTRIAL APPLICABILITY

According to the present invention, a polyol-crosslinkablefluorine-containing elastomer composition which is excellent in fuelresistance (especially biofuel resistance), chemical resistance andsolvent resistance (especially resistance to an acidic solvent) and iscrosslinkable at the same crosslinking speed as in the case of usingcalcium hydroxide in a necessary amount even without blending calciumhydroxide (or even if an amount of calcium hydroxide is decreased) whichincreases the crosslinking speed but accelerates oxidation anddeterioration of a fuel.

1. A fluorine-containing elastomer composition comprising apolyol-crosslinkable fluorine-containing elastomer, a polyolcrosslinking agent and a silicate of an alkali metal.
 2. Thefluorine-containing elastomer composition of claim 1, wherein thesilicate of an alkali metal is sodium silicate or a salt hydratethereof. 3.-7. (canceled)